1. The Field of the Invention
The present invention relates to improvements in firing ovens for ceramic material for a refractory oven. Particularly, the invention refers to improvements in roller firing ovens for plate-like materials, in particular ceramic tiles, wherein the materials being fired travel along the oven because they bear on rotating rollers which impart thereto forward motion at a desired speed.
Such ovens may be constituted by a single channel or by one or more superimposed channels, and the invention is applicable in the same way to any number of channels, the only thing requirement being to multiply the same means required for a single channel.
Reference will be made in the description to an oven for firing ceramic tiles, though this does not constitute a necessary limitation. Since the invention is advantageously applicable to an oven of this kind, which forms the object of the copending application No. 27995 A/76, reference will be made in the present description specifically to an oven of such type, but this reference does not constitute a limitation as the invention is generally applicable to any roller oven for firing of materials having a plate-like configuration.
Ovens of such a type are schematically constituted by one or more channels, generally having a substantially rectangular cross-section, wherein rollers having their axes perpendicular to the longitudinal axis of the channel, i.e. to the direction of travel of the material being fired, are disposed at suitable intervals, such rollers being actuated for rotation by suitable mechanical drive means. The plate-like materials to be treated, in particular the tiles (to which reference will be made hereinafter for illustrative purposes) are laid onto the rollers at the channel inlet and are advanced thereby at a linear speed substantially equal to the peripheral speed of the rollers. The value of this speed is irrelevant to the invention, but generally, in modern ovens, may be in the order of one meter per minute or more. The heat required for the heating and firing of the tiles is communicated thereto in various ways depending on the oven, and in particular by convection, by radiation or by a combination of convection and radiation. The heating by radiation is effected by bringing the ceiling and the floor to a suitable temperature for directing radiation onto both faces of the tiles the walls also assuming high temperatures in order to maintain the thermal balance of the environment. The heating by convection is effected by introducing into the firing chamber, constituted by any one of the described channels, a hot gas, which may be any gas but is generally constituted by the combustion fumes of suitable burners mixed with excess air. The fumes may be introduced into the firing chamber in any suitable way, i.e. laterally or from the ceiling and/or the floor, or from all sides, and are generally possessed of a longitudinal flow along the firing chamber, generally countercurrent to the travel of the tiles.
In the oven described in earlier application No. 27995 A/76, the tile advancing rollers are not located on the center line of the vertical cross-section of the firing chamber but are shifted upwards with respect to such line, i.e. are closer to the ceiling than to the floor of the oven.
The invention will be described in its practical application to an oven having the aforesaid characteristics, but it is not limited thereby and would be applicable to a different roller oven as well.
2. The Prior Art
One of the most serious problems which arise in the industrial use of ovens of the type described, is constituted by the possibility, which it is impossible to entirely eliminate, of breakage of the pieces being fired, e.g. tiles. Such pieces when they break, give rise to fragments having dimensions such that they may pass between the advancing rollers and therefore they fall onto the oven floor. Further, detritus and dust originating from the fired material accumulate on such floor. Possible results may be, if the firing chamber is not periodically cleaned, obstructions in the firing chamber which produce even production stoppages, and a deterioration of the quality of the products due to the deposit thereon of the dust and the detritus set in motion by the gases flowing along the firing chamber.
To obviate these inconveniences, at least in part, it is necessary to periodically stop the oven and clean its floor, an operation that is not easy due to the considerable length of the firing chamber. In practice, however, even periodic cleanings, economically burdensome because of the labour required and especially because they interrupt the production, do not completely eliminate the obstruction of the firing chamber and the deterioration of the quality of the product. On the contrary, it often occurs that the necessity of cleaning the firing chamber before the moment planned in the production program, is made evident by the obstruction of the chamber itself and the fact that the pieces being fired do not advance regularly, with the result that the loss due to the production scrap thus generated is added to the cleaning costs.
All these inconveniences are eliminated by the present invention.